Research On The Coupling Characteristics Between Slot SPP Mode And Dielectric Waveguide Mode

Surface plasmon polariton (SPP), which is a kind of specialelectromagnetic phenomenon, has shown some novel characteristics andsignificant applications in the field of integrated optics, bio-chem sensing,energy harvest and so on.Slot surface plasmon polariton (Slot SPP) with highly compact fieldshows unique advantages in applications for ultra-compact photonic devicesand highly sensitive sensor. In this paper, the excitation, transmission,coupling and sensing characteristics of the Slot SPP mode are analyzedtheoretically and related fabrication process is studied preliminarily. Theachievements are as follows:A hybrid coupler composed of a Slot SPP waveguide and a dielectricwaveguide is proposed. Based on the finite element method and modeexpanding method, the coupling characteristics between the Slot SPP modeand dielectric waveguide mode are analyzed. The simulation results indicatethe TE mode of the dielectric waveguide can couple to the Slot SPPwaveguide with the mode size compressed to55nanometers at λ0=1.55μmwithin the coupling length of just several microns. This provides not only anintegratable route to excite Slot SPP mode efficiently, but also an interfacebetween the Slot SPP devices and dielectric devices.A scheme of refractive index sensing for ultra-thin detecting layer is alsoproposed based on the hybrid coupler. And the sensing characteristics fordetecting layer with different thicknesses are analyzed theoretically. Thecalculation indicates, the sensitivity can be high as~3.5×10-6RIU, even whenthe thickness of the detecting layer is just70nm. Also, the sensing region andsensitivity can be adjusted by varying the width of the dielectric waveguideand the distance between the two waveguides. At last, the fabrication process of the hybrid coupler is studiedpreliminarily. The Slot SPP waveguides with the width from40nm to200nmare obtained by FIB. And SU8, which is a kind of photoresist, is spun andcured as the cladding matching layer between the Si waveguide and the SlotSPP waveguide. By this way, the Si waveguide is perfectly buried and a flatsurface of the cladding matching layer can be obtained. The aboveachievements lay a good foundation for the further fabrication of the hybridcoupler.